Process for recovering potash salts from liquors containing borax



Aug. 8, 1933. c. F. RITCHIE Er AL 1,921,481

PROCESS FOR RECOVERING POTASH SALTS FROM LIQUORS CONTAINING BORAX Filed July 16, 1929 spect. to boraxi Patented Aug. 8, 1933 1,921,481 PROCESS, FORRECOVERHNGPOTASH SALTS mom LIQUQBS CONTAINING BORAX Charles F. Ritchie, William A. Gale, and William E: Allen, Trona, Calif., assignors to American Potash &- Chemical Corporation, Trona, Califl, a Corporation of Delaware Application July 16, 1929. Serial No. 378,745

' ielola ms. (o1. 23-41)- This invention relates to certain processes and equipment utilized in the separation of potassium" chlorid, (potash), from liquors containing the same, togetherwith borax. In particular, this invention relates to process procedure and equipment'involved in-the precipitation of potash from liquors which likewise contain suflicient boraxto' cause, undernorma'lconditions of operation', a" precipitation of both potash and borax.

Oneob'ject of the'present invention is to providefan" efiicient and economical system for rapidlycooling a hot concentrated solution of potassium chlorid' and borax', thereby bringing, about precipitation of potassium chlorid and simultaneously producing a state of supersaturation with respect toborax Another object of the invention istoprovide a' system in which the. desired results may be achieved to the best advantage; at the same time producing crystals of potassium chlorid of superiorquality With respect tosize' Other objects and advantages of the invention willappear as the description proceeds;

While the" present invention is described in 7 liquorvery rapidly,potash may be caused to sepa rate Without substantial precipitation of hora-x. The faster the cooling and the shorter the time ofsubsequent retention of the supersaturated liquonthe greater will be the satisfaction derived fromthe process.

The. desirabiliy of evaporative cooling procedurehas been known for some time; "its advantages, as applied to the rapid cooling or" potash liquor, are set forth herein, together with such improvements to. equipment, of the prior art, specified in' United States Letters Patent No. 1',676;277, as render the equipment most efficient for producing results superior to those heretofore obtainable. 7 Hotconcentrated liquor containing potash and borax'maybeproduced by the high temperature evaporation of Searles' Lake or like brines, A similar'liquor may also be produced by the high temperature leaching of solar evaporation salts,

By cooling hot concentrated boraxr Hot concentrated liquor resulting from the high temperature evaporation of SearlesLake brine, together with certain end liquors from previous manipulations, may have the following percentage composition, when ready for cooling for potash precipitation:

KCl 18. 8 Na2B40'1 5; 9 NEL2B2O4 1. 2" NLzCOs 7. 8 N9J2SO4 '1; 7 v NaCl 7. 1 Unreported f 2. 6- Water 54. 9

' Total 0% For the most efiicient operation of aprocess recovering potash and borax 'froni Searles Lake and similar brines, it is the practice to'produce a hot concentrated liquor essentially saturated With the. potassium compound. Other components appear in the hot concentrated liquor in such? quantities as may result from-the phase rulesolubilityrelationships or as maybe vdetercontaining valuable quantities of potash and 15 mined by the relative quantities in the original brine. A small quantity of water is usually added to the concentrated liquor to-compensate the water evaporated, thereby preventing the precipitation of undesirable salts upon evapora-s moval'of the precipitated potash, by meansof a filter or a centrifugal machinetheborax iscaused to precipitate by seeding, furthercooling or prolonged retention, and thereafter removed-from the liquor. The remaining motherliquoncontaining valuable potash and borax concentrations, is returned to the evaporation or leach system. I We have carried out therapid coolingofhot concentrated potash liquor in the conventional type of heat transfer equipment; for example, in

loo

While such equipment .pro-. v

evaporative cooling equipment is far superior, both with respect to economy of equipment and operation and also with respect to the results produced. While the advantages of an evaporative cooler are manifold as compared with indirect coolers, its greatest advantages, in the present instance, reside in the following: provision 'of a hermetically sealed system, freedom from excessive crystal. deposits and large handling capacity, resulting in relatively short time of liquor retention.

Wehave found that one of the contributing causes to the destruction of the supersaturation of liquor with respect to borax is the infiltration of borax laden air into the cooling tanks. In a plant manufacturing borax, it is impossible to prevent a certain amount of fine borax from being dispersed into the air. When fine borax crystals are brought into contact with liquor supersaturated with respect to borax, the liquor is said to become inoculated, and crystallization ensues. In the old style cooling tanks, which were usually open to the air and operated in a discontinuous or batch manner,'the supersaturated liquor often became seeded, and borax crystallization resulted. The use of continuous evaporative cooling equipment to a large extent, prevents trouble from this source. In continuous, reduced-pressure, evaporative cooling equipment outside air, usually laden with borax particles, is rigidly excluded. Hence the maintenance of borax supersaturation in the liquor, so vital. to the successful operation of the process, is more easily and completely realized in evaporative cooling equipment, than in the indirect-cooling equipment of the prior art.

Excessive crystal deposits which form upon heat transfer units of the conventional type of indirect coolers constitute a liability to smooth,

continuous operation. Wash water must be supplied-for the removal of such deposits, thereby causing a loss of the valuable crystals, as well as holding up operations, involving extra labor expense, et cetera. The use of properly designed evaporative cooling equipment, such as that specified in United States Letters Patent No. 1,676,277, almost entirely eliminates the formation of crys-' tal deposits. Furthermore, due to the mechanism of the heat transfer involved in the latter case, excessive local cooling is prevented.

The present inventors have successfully operated such equipment for long periods without appreciable crystal deposition. Furthermore we have found that more complete and dependable supersaturation of the liquor with respect to borax may be maintained than with indirect coolers. The use of evaporative coolers has proven eminently more satisfactory for conducting the process of United States Letters Patent No. 1,343,401, than coolers known to the prior art.

Time is the essence of the above process. Due to the inherent features of indirect coolers it is difficult to cool large volumes of liquor in much short of 1-2 hours. Although desired results were obtainable by this method. it often happened 'that, for one cause or another, the supersaturation of the liquor was destroyed and borax crystallization took place. Suchoccurrences, of course, required the rejection of a certain amount of potash, as well as a complete washout of the system with hot water. The capacity of evaporative cooling equipment is materially greater than indirect cooling equipment, due in part to the better heat transfer mechanism involved and likewise to the fact that the efliciency of heat transfer remains constant regardless of the length of time the equipment has been in operation. In the old style indirect coolers, fitted with an excessively large cooling area, from 1 to 2 hours was requiredto cool a 3000 gallon batch of liquor. We have operated a normally designed evaporative cooler, holding 3000 gallons of liquor over extended periods at the rate of 100 gallons per minute, with results far superior to those obtained in the former case. The average time of retention of liquor within such a cooler is theoretically 30 minutes. For carrying out the process of United States Letters Patent No. 1,343,401, evaporative coolers are in many ways superior to indirect coolers.

By the process of the present invention, hot concentrated potash liquor is cooled from its high temperature of production to the desired low temperature entirely by evaporative cooling. Furthermore, said cooling is accomplished in two steps, both embracing evaporative cooling. This scheme possesses a combinationof practical advantages over prior efforts Where the operation has been attempted in a single step, or by other means different from the present invention.

l-Iot concentrated liquor produced, from searles Lake or similar brines, for the recovery of high grade potash is essentially saturated with KCl at a high temperature, ZOO-240 F. However, such liquor seldom contains sufiicient borax to produce saturation .at that temperature. The liquor of the above analysis was found to be saturated with respect to borax at approximately 130 F.; this temperature will, of course, differ with variations of the processes employed but'it' is advantageous to maintain it as low as possible. We take advantage of this fact in the operation of the improved process of this invention. By 0001- a ing only to the saturation point, with respect to borax in the first step of evaporative cooling no liability of crystallizationis incurred. The system is hermetically sealed; so no borax seed is allowed to enter the system, causing precipitation of borax in the subsequent cooling step. In this cooling from 200-230" F. to approximately 130 F. the greater portionof the sensible heat of the liquor and the greater portion of the potash available is precipitated. Since borax crystallization is impossible at this temperature, equipment such as. that specified in United States Letters latent No. 1,676,277 may be successfully employed.

The advantages of such equipment for cooling, in general, have been set forth hereinabove. The advantages of the circulation of sludge, as provided by that equipment are set forth below in connection with certain improvements we have made to that end.

We have found that, aside from the various factors, hereinbefore mentioned, contributing to the destruction of the supersaturation of borax, there exists another factor which is likewise very active. This is the force known to those of the crystallization art as mechanical stimulus. The phenomena of mechanical stimulus is utilized by nearly every chemist who, desiring to bring about precipitation of a supersaturated component, scratches the sides of a beaker with a stirring rod its or similar object. We have found that mechanical stimulus may be brought into play in comlengths of pipe lines is effective in destroying the supersaturation characteristics of the component in question (borax). We do not'believe this effect due to an unreasonably long time of retention; for the effect is even more pronounced as the rate of flow of the sludge of potash and liquor supersaturated with borax is increased within the pipes. It is one of the purposes of the process of this invention to provide means for rapidly cooling potash liquor, simultaneously supersaturated with respect to borax, in which mechanical stimulus is reduced to a minimum.

In the preferred form of our invention we employ a condensing medium consisting of a saturated brine, of the lowest temperature economically obtainable, for producing the desired reduction in temperature in the final evaporative cooler. The use of this improved condensing medium has enabled us to carry the temperature of the liquor 12 F., or more, lower than would have been possible with condenser water of economical origin.

By this method We are able to conduct the cooling of concentrated potash liquor containing borax to the desired temperature without the use ofexpensive artificial refrigeration, as has been required under certain conditions of past practice.

Furthermoraby combination of the aforementioned improved condensing medium, together with the improved equipment of this invention, we are able to produce a most satisfactory degree of supersaturation of borax within the liquor. In the equipment of our invention the final cooling is carried out in such a manner that forces producing mechanical stimulus are reduced to a minimum. e

The present invention, together with various objects thereof, will best be understood from a description of one form or example of a process embodying the invention. There is, therefore,

hereafter described with reference to the accom-.

panying drawing the preferred form or example of a process and apparatus embodying this invention.

Inthe drawing, Figural shows an elevation of a suitable secondary evaporative cooler, having a section cut away to show certain interior construction, and Figure 2 represents a plan of the same taken through line 2-2. Fig. 3 shows an elevation of the settler and certain associated parts, portions being broken away. Fig. 4 shows a diagrammatic elevation of the combination of equipment for carrying out the process.

Referring to the drawing, we provide a relatively small chamber 1, having considerable dome space above the point of liquor inlet 2, to prevent :undue' splashing and entrainment of the liquor Liquor enters the cooler continuously through port '2, is immediately cooled and passes out through outlet valve 4. Level of the liquor is maintained as shown by the dotted line 22,at or near the level of the inlet port 2. As a specific example of one piece of equipment and a pro-' 1 cedure which we have employed for this final or secondary cooling, the followingis given. Liquor "at the temperature of '130" F. was delivered to the secondary cooler, Figure 1, at the rate of approximately. 150 g. p. m. The bottom of the cooler comprised a 52 circular cone as shown by 5 of Figure 1. The level of the liquor was held to such a height that the cone contained approximately 600 gallons during normal operating conditions.

Liquor was cooled by evaporative means to 90 F.

The time of retention was therefore approximately 4 minutes. Circulation and other effects producing mechanical stimulus were reduced to a minimum. The difficulties encountered with processes and equipment prior to the inception of this invention are entirely overcome by this scheme, a most .desirable and dependable supersaturation with respect to borax being maintained at all times.

While in the past the element of time andvarious physical elements have been believed to be the controlling factors in the production of a satisfactory degree of supersaturation with re-' spect to borax, we have found that a certain physical chemical phenomenon is also involved in the process. Two hydrates of borax are known to exist between the cryohydric point and the boiling point of saturated solutions underordinary pressure conditions. These hydrates'are the pentahydrate (NazBsOmEHzO) and the deca- The transition point hydrate (Na2B4OL1OI-I2O) of the hydrates in pure water is approximately 143F. In complex liquors such as those resulting from the evaporation and manipulation of'Searles Lake and similar brines, the transition temperature is materially lowered. The transition temperature of the pentahydrate to decahydrate in liquor of the preceding composition has been found to be approximately 86-90 1*". At temperatures above the transition point the pentahydrate is stable and will be precipitated when borax is crystallized above this temperature. At temperatures below the transition point the decahydrate is stable and will be crystallized when borax is crystallized below this temperature;

We have found that the supersaturation of borax is much less stable at temperatures favor- I able to the formation of decahydrate borax than at temperatures favorable to the formation of pentahydrate borax, the degree of supersaturation being constant. In other words it has been found much easier to produce and maintain a supersaturation of 5 percent NazE Oq at Sill-100 F. than to produce and maintain a supersaturation'of 5 percent in the temperature regionof "-85" F.

Since it is the usual practice to recycle liquor back to the evaporator or leach system after 'removing a cropof potash and borax, it may be seen that it makes little difference from an efiiciency standpoint whether the liquor be cooled slightly above or slightly below the transition point. However, from the standpoint of maintaining a satisfactory degree of supersaturation within the liquor being cooled this point is of paramount importance. Hence for the purpose of precipitating potash from concentrated liquor and simultaneously incurring a satisfactory supersaturation; with respect to borax,.we have found it advisable in the preferred form of this invention it is specified that the liquor be cooled only to a minimum approximating the transition point of the two hydrates of sodium tetraborate.

The present invention provides means for economically and rapidly cooling hot concentrated potash liquor containing borax, wherein a most satisfactory supersaturation of borax is maintained. The success of the present invention resides largely in the means provided for avoiding destruction of supersaturation by mechanical stimulus. The equipment of the present invention provides further means for maintaining the desired supersaturation between the point of its production and the point of separation of potash from the cold sludge.

When liquor of the preceding composition is cooled as specified herein, to a minimum of 86 1 the resulting sludge of supersaturated liquor and potash crystals contains approximately 1.1 pounds of potash crystals per gallon of sludge, or approximately 10% solids by Weight. Such a sludge is thinner than can be satisfactorily handled in commercial filters or centrifugals. In order to provide a thicker sludge for such equipment it has been found necessary to thicken the attenuated product obtained from the coolers. This step not only produces a more satisfactory sludge for centrifugal or filter feed, but also removes a large proportion of the supersaturated liquor from the sphere of the precipitated potash, thereby reducing the possibility of precipitation of borax.

It has been pointed out that liquor supersaturated with respect to borax has been found to be very susceptible to mechanical stimulus produced by pumps. In order to avoid this undesirable effect we so arrange the secondary cooler of this invention with respect to the settling or thickening equipment, that no mechanical handling will be required. Referring to Figure l, the cooled liquor is passed continuously from the secondary evaporative cooler 1, down line 6 to a suitable settler 7 of Figure 3. We prefer to employ a settler of the simplest possible construction. Since undue liquor retention is not desired, the volume of the settler is maintained as small as'possible. A 45 or 66 conical section has been found quite satisfactory for this service.

Agitators or scrapers are avoided unless the nature of the sludge is found to be such as to re quire their installation within the settler.

The secondary evaporative cooler 1 of Figure 1 is placed above the settler 7 of Figure 3, in

such a manner that sludge will flow by gravity into the settler. The elevation of the cooler above the settler is such that the column of liquo1 in the connecting line 6 Will be sufiicient to balance the reduced pressure inside the evaporative cooling equipment with the existing atmospheric pressure.

Referring to Figure 3, pipe 6 terminates into a distributing cup 8 placed beneath the surface of the liquor in the settler 7. This cup or similar device serves to deflect the downward force of the liquor, preventing undue turbulence in the lower portions of the settling cone. As sludge is passed through cup 8 into the settler 7, liquor flows from th center toward the outside edge and into launder 9 from whence it may be withdrawn through outlet 10. A leveling ring 11 may be provided for causing uniform distribution of the overflowing liquor, or other similar devices may be employed. As liquor passes transversely from the central cup 8 toward the launder 9, potash crystals settle into the bottom of the cone.

A thickened sludge may be withdrawn at the bottom by means of a valve 12, a suitable orifice, a balanced density valve or other similar mechanisms. In'this manner we are able to combine the usual barometric seal with the necessary settling equipment, thereby obtaining resultssuperior to those heretofore obtainable. The elimination of pumps, made, possible by this combination, has eliminated difficulties previously encountered, resulting from the destruction of the borax supersaturation of the cold liquor by mechanical stimulus.

The equipment of United States Letters Patent No. 1,676,277 has been found to be well suited to the primary cooling of hot concentrated potash liquor to the point of saturation with borax. During such cooling a large proportion of the available potash is precipitated. In order to increase the efliciency of the subsequent settling operations as well as those of filtering or centrifuging and drying, it is desirable to produce a potash crystal of relatively large size and good structure. It has been found that if concentrated potashliquor be subjected to flash evaporation (cooling) very fine crystals are produced. The thermal circulation specified in the above mentioned patent, has been found of value in producing relatively larger potash crystals than those obtainable when flash evaporation is tolerated. Large amount of cold liquor is mixed with small amount of hot liquor, thereby preventing undue flashing.

Other advantages of the circulation of liquor have also been set forth. We have found that if a small quantity of hot concentrated liquor be mixed with a large quantity of cooled liquor containing suspended potash crystals and the resulting mixture at a relatively low temperature 'be introduced into the evaporative cooler, the

ebullition takes place in a regular and orderly manner. The presence of the large quantity of potash crystals, provided by such circulation, causes the potash content of the hot liquor to be deposited, to a large extent, upon the potash crystals already present resulting in the production of the desirable large crystal potash.

We have been able to increase the desirable effect of sludge circulation in the primary step of the process of evaporative cooling by supplying a pump in the closed circuit comprising the depending legs and the evaporative cooler. Referring to Figure 4, the prescribed circulation pump is shown as 22 placed in the closed circulation system comprising pipes 21. Heretofore thermal circulation has been employed- While for the most part satisfactory, the rate of flow, in many cases, has been found to be insufficient for bringing out the maximum desired effects. Also in the case of thermal circulation some difficulty has been experienced with short circuiting; a reversal of flow direction taking place probably due to slight obstructions in the discharge side of the closed circulation system, resulting in hot liquor being passed from the system through the outlet normally handling cooled liquor. The satisfactory utilization of forced circulation in the primary step of evaporative cooling of hot concentrated potash liquor containing borax is made possible by limiting the temperature of cooling therein to the temperature of saturation with respect to borax. By this method all possibility of borax precipitation is eliminated and conditions most favorable to thecrystallization of potash .may be realized.

Large size equipment may be employed, thereby standard design. i In the particular process o thi reducing the capital outlay required. For example, we have found that a primary evaporative cooler suitable for cooling 100 gallons per minute of hot concentrated potash liquor from 230 F..to 130 F. may be of 3000 gallons (net) capacity. The average time of retention of liquor within the cooler is theoretically 30 minutes. However, due to the continuous mixing and circulation, some liquor is retained even a greater length or" time. Such equipment, if operated for cooling to the desired low temperature in a single step is not satisfactory; crystallization of borax being the inevitable result.

The foregoing sets forth the nature and advantages of the process of this invention as applied to the problem of producing satisfactory potash crystals from hot concentrated liquor containing the same together with borax, simultaneously incurring a satisfactory supersaturation in the liquor with respect to borax. The elevation of Figure 4 sets forth a combination of equipment in its proper order, suitable for carrying out the improved process of this invention. I

In Figure 28 represents 'a suitable tank for storing the hot concentrated liquor essentially saturated with potash and containing appreciable quantities of borax. Liquor is withdrawn from this storage tank by means of a pump 26. In the preferred form of the invention we employ a constant level tank 24 for maintaining a continuous, constant, automatic feed to the primary evaporative cooler. Such a tank, of suitable design, is supplied with hot liquor by a pump 26, in excess of that required by the cooler. Excess liquor flows back through a line 27 to the storage tank 28, or into the suction side of the pump 26, as shown. The constant level tank 24 is so placed with respect to the evaporative cooler 30 that'the reduced pressure will maintain the level of liquor therein at'a predetermined height.

In accordance with the'advantages hereinbefore described, a pump 22 is employed for'circulating sludge from the primary evaporative cooler, mixing it with a small proportion of hot liquor and returning it to the evaporative cooler. To

'thisend hot liquor from the constant level tank 24 is led into the suction side of the circulation pump 22. I

In the layout herein described the circulation pump 22 is made of 600 gallons per minutecapacity. One hundred gallons per minute of hot liquor are introduced through line 23, the warm mixture entering the evaporative cooler at some convenient point, as shown at 29.

The inlet port 29 may be caused to enter the chamber 30 tangentially thereby producing a swirling motion of the contents thereof, causing thorough mixing and preventing excessive splashing and foaming. Level of the liquid is usually maintained considerably above'the point of inlet 29, the evaporativecooler being designed to allow sufiicient .dome space for preventing excessive splashing and entrainment of liquor with the vapors passing out through line19. ,By maintaining the level of liquid considerably above the inlet 29 splashing isavoided even when a rapid circulation ofbrine is employed. A single primary'evapor'ative' cooler of the present invention may contain approximately 3000 gallons ,of liquor, the cylindrical section being 8Jfeet. in

diameter. 7

A separator 31 is provided :for recovering liquor passing over with the vapors, and is con- A vacuum pump or jet exhauster, not shown,

usually provided in conjunction. with the barometric condenser ior the removal of noncondensable gases.

Liquor is cooled in the chamber of the primary evaporative cooler 30 to a temperature approxie mating the point of saturation with respect to borax, i. e., under the aforementioned conditions, ai oximately 13 F, Cooled liq r (slud e) is removed by means of line 15 and pump 1% and delivered to the second step of the improved evaporative cooling process of this invention via lines 16 and .Liquor tra e in th separator 31 may also be returned by means of a suitable line to the suction side of the transfer pump 14, or th r suita l di po it o may b m de ihe eoi,

While s ud e m y b obta n o deliv r to cooler 30 is delivered continuously to the second ary evaporative cooler 1. Details of the construe tion and operation of the secondary evaporative cooler have been set'forth hereinbefore and are illustrated in'Fig'ures 1 and 2. Only a small volume of liquor and no circulation or undue agitae tion are maintained in thesecondary evaporative cooler. In the case which has been successfully operated and is being described, 150 gallons per minute of liquor at approximately F. are supplied from primary evaporative coolers. Liquor level is maintained within the'5 2 corneal secti n appr imately at th l vel o the in et po t 30a; aboutfioo g l n o l qu r being withheld.

A separator 33 is provided for recovering liquor entrained with the vapors passing off the cooler through vapor line 3 The separator is eon- .nected with a baromet ic condense 5 .by means of vapor line 3,6.

Barometric condenser 35 may be of standard design. In the preferred form of this invention w s vice the barome ric o enser 35 w th a saturated brine. By th use o this saturated brine in place of the usual medium (water) we are able to maintain the temperature of the liquor within the secondaryevaporative cooler 1 at least 12 F." lower than is p ibl with Water .atihe same temperature. In this second cooling step of this improved processliquoris cooled to a temperature approximating the transition point of the two hydrates of borax, or in the .presentliquor to'approximately 90 F.

Cold liquor passes continuously from the sec.- ondary evaporative cooler 1 through line 6 into the continuous cone settler '7. The advantages and design of the settler 7 have been described hereinbefore and are illustrated by Figure 3. Within thesettler 'l the large crystals of potash produced for the mostpart by the cooling and manipulation within the primary evaporative cooler .30, settle rapidly to the bottom, from whence they may ,be removed as ,a thickened sludge for ,the .finalf recovery of high grade potash. Clear liquor overflows and is utilized in i as suitable processes embracing the recovery of borax, the end liquor being returned to the evaporation or leach system for further recovery of the valuable constituents.

. Figure 4 and the description thereof represents in a somewhat conventional manner the improved processor the present invention. It must be understood that only single units have been shown and many common devices used in connection therewith have been eliminated for the purpose of simplicity. In commercial practice we may. employ a series of primary evaporative coolers in parallel, thereby lending flexibility to the system. The same is true in the case of the secondary evaporative coolers. In a specific installation, we have employed three primary evaporative coolers in parallel, feeding 100 g. p. m. of liquor to each, followed by two secondary evaporative coolers in'parallel, feeding 150 g. p. m. of the partially cooled liquor to each. Other combinations may be made without departing from the scope or the present invention.

Observation ports, level gauges, thermometers, regulation valves, vacuum regulators, et cetera, have been omitted from the description, since such equipment is of common knowledge and always employed by competent engineers in the design of such equipment, where required.

The apparatus herein described is made the subject matter of a copending divisional application.

We claim:

1. A process of cooling hot liquors to precipitate one of two constituents which exceed their saturation value on cooling, one of which has a tendency toward supersaturation, which comprises rapidly cooling the liquors beyond the point of saturation with respect to both by evaporation under reduced pressure. I 2. 'A process of cooling hot liquors to precipitate one of two constituents which exceed their satu ration value on cooling, one of which has a tendency towards supersaturation, which process comprises rapidly cooling the liquors by evaporation under reduced pressure beyond the saturation value of both constituents to thereby form a sludge of one of the constituents by holding the other constituent under supersaturation, and separating remaining liquor from the precipitate by maintaining the liquor free from mechanical stimulus.

potash and borax to precipitate the potash while maintaining the borax in supersaturation, which comprises rapidly cooling the liquors by evaporation under reduced pressure beyond the saturation value of both the potash and borax to thereby form a potash sludge, while holding the borax in supersaturation, and separating the remaining liquor from the potash sludge while maintaining the liquor free from mechanical stimulus.

5. A process of cooling hotliquors to precipitate one of two constituents which exceed their saturation value on cooling, without, precipitating the other, the former constituent reaching its saturation value on cooling previous to the second.

constituent, which comprises first cooling the solution to substantially the point of saturation with respect to the latter constituent, thereby forming a sludge of the first constituent, and thereafter rapidly cooling the liquor beyond the point of saturation with respect to the other constituent by evaporation under reduced pressure while maintaining said'latter constituent in a state of super saturation.

6. A process of cooling hot liquors to precipitate one of two constituents which exceed their saturation value on cooling without precipitating the other, one'of said constituents exceeding its saturation value previous to the other constituent, which comprises subjecting the solution to rapid evaporative cooling to approximately the saturation value of the solution with respect to the second mentioned constituent, while rapidly mixing the hot liquor with a coldliquor resulting from said evaporative cooling, and then subjecting the liquor to a second stage of evaporative cooling in which the liquor is cooled beyond the point of saturation with respect to said second constituent, while mechanical stimulus is prevented and said second constituent is maintained in a state of super saturation.

7. A process of cooling hot brine containing potash and borax, the potash content of the brine exceeding its saturation value when the brine is cooled previous to the borate content, which process comprises subjecting the hot brine to evaporative cooling to approximately the temperature of saturation of the brine with respect to the borax, while rapidly mixing the fresh hot brine to be cooled with'the cold brine resulting from said step of evaporative cooling, and then subjecting the liquor to a second stage of evaporative cooling beyond the point of saturation with respect to said borates, while preventing mechanical stimulus, and maintaining the borates in a state of supersaturation.

8. A process of cooling hot liquors to precipitate one of two constituents which exceed their saturation value on cooling, without precipitating the other constituent, which process comprises rapidly cooling the liquors beyond the saturation value of both constituents by evaporative cooling, without substantial mechanical stimulus, so as to hold one of said constituents in a state of super saturation, and then passing the precipitated sludge of the other constituent by gravity to a settling zone wherein liquor is separated from said sludge and the same thickened.

, 9. A process of precipitating potash from a hot I brine containing potash and borax, which comprises subjecting the hot brine to evaporatlve cooling while precipitating the potash, whereby to 'cool the brine to substantially the point of saturation with respect to borax, and then subjecting the brine to a further stage of evaporative cooling while precipitating further potash and. maintaining the borax in a state of supersaturation, such second stage of cooling being carried out to substantially the transition'point between I the pentahydrate and decahydrate of ,borax.

10. A process of precipitating one of two constituents of a hot liquor which exceed their saturation valuewhen the liquor is cooled, which process comprisessubjecting the liquor to cooling while enclosing the liquor from the atmosphere to prevent seeding, the cooling being continued beyond the saturation point of one constituent, thereby precipitating such constituent,

and to approximately the saturation point of the otherconstituent, and then subjecting the liquor rapidly to evaporative cooling beyond the saturation point of the second constituent while preventing mechanical stimulus, and holding the second constituent in a state of supersaturation.

11. A process of precipitating from hot liquor one of two constituents which exceed their. saturation value when the liquor is cooled, which process comprises subjecting the liquor to evaporative cooling while forcibly circulating the liquor from the evaporating zone through a mixing point and back into said evaporating zone, passing fresh hot liquor to be cooled. into said forcible circulating stream at said mixing zone, said evaporative cooling being continued to approximately the point of saturation with'respect to one of said constituents while exceeding thesat uration point of the other constituent and precipitating the same, and then subjecting the liquor to a second stage of evaporative cooling continued beyond the saturation point of said first constituent, while avoiding mechanical stimulus, and maintaining said constituent in a state of supersaturation.

12. A process of evaporative cooling of a brine containing two salts which exceedtheir saturation value on cooling, one of said salts having a tendency towards supersaturation, which process comprises subjecting the brine to evaporative cooling while agitating the brine to commingle the hot fresh brine with the cold brine resulting from said evaporative cooling, said evaporative cooling reducing the temperature of the brine to nearly the point of saturationwith respect to said constituent which has a tendency towards supersaturation, and then subjecting the brine to further evaporative cooling with less agitation, wherein the temperature or" the brine is reduced to the point of supersaturation or" said constituent which has a tendency towards supersaturation.

13. A process of separating potash from brine essentially saturated in salt and potash and containing borax in sufiicient quantity that the borax exceeds saturation after cooling, which process comprises diluting the brine to compensate for evaporation, subjecting the brine to evaporative cooling while rapidly mixing alarge amount or" the cooled brine with the fresh hot brine, said evaporative cooling being suflicient to approach substantially the saturation value of the brine with respect to borax, and then subjecting the brine to a further step of evaporative cooling, while avoiding mechanical stimulus, said evaporative cooling being, continued until slightly above the temperature of the transition point of pentahydrate to the decahydrate of borax.

14. A process of separating potash from brine essentially saturated in salt and potash and containing borax in sufficient quantity that the borax exceeds saturation after cooling, which process comprises diluting the brine to compensate for evaporation, subjecting the brine to evaporative cooling while rapidly mixing a large amount of the cooled brine with the fresh hot brine, said evaporative cooling being sufficient to approach substantially the saturation value of the brine with respect to borax, and then subjecting the brine to a further step of evaporative cooling, while avoiding mechanical stimulus, said evaporative cooling being continued until slight- 1y above the temperature of the transition point of pentahydrate to the decahydrate of borax, and passing the potash sludge through a separation zone in a smooth flowing stream wherein brine is separated therefrom and the sludge thickened.

15. A process or" precipitating potash from hot concentrated brine containing the same, together with borax, which comprises continuously passing the brine to a primary evaporative cooling zone wherein the brine is cooled and caused to precipitate potash, said cooling being carried approximately to the point of saturation with respect to borax, continuously circulating cold brine from said primary evaporative cooling zone forcibly through a mixing zone and back into said cooling zone, continuously passing hot liquor to said mixing zone to be admixed with said cold 190 liquor and passed to said cooling zone, and continuously passing the cooled brine containing potash crystals in suspension to a secondary evaporative cooling zone wherein said brine is cooled while mechanical stimulus is avoided, and wherein said brine is maintained for only a short time, wherein further precipitation of potash is eiiected and supersaturation of the liquor with respect to borax is incurred.

16. A process of precipitating potash from hot concentrated brine containing the same, together with borax, which comprises continuously passing the brine to a primary evaporative cooling zone wherein the brine is cooled and caused to precipitate potash, said cooling being carried approximately to the point of saturation with respect to borax, continuously circulating cold brine from said primary evaporative cooling zone forcibly through a mixing zone and back into said cooling zone, continuously passing hot liquor to said mixing zone to be admixed with said cold liquor and passed to said cooling zone, and continuously passing the cooled brine containing potash crystals in suspension to a secondary evaporative cooiing zone wherein said brine is cooled while mechanical stimulus is avoided, and wherein said brine is maintained for only a short time, wherein further precipitation of potash is efiected'and supersaturation of the liquor with respect to borax is incurred, and continuously passing the cold brine from said secondary evaporative cooling zone to va settling zone wherein brine is continuously separated from the potash sludge and in which mechanical stimulus is avoided.

CHARLES F. RITCHIE. WILLIAM A. GALE. WILLIAM H. ALLEN. 

